Pearl Harbor was a military base on the island of Oahu, but in 1941 Hawaii was not a state. Hawaii signed a treaty in 1875 allowing the United States to use Pearl Harbor as a military base. Pearl Harbor was the best place to defend because of how it was laid out. First, in the center of the harbor there was Ford Island, which has a lot of the military installations, and there are docks that hold ships positioned all around it. Second, the water was very shallow, so it was easy to spot potential enemies coming into the base. Finally, the only way in by water was a narrow channel leading right into the thicket of the base, and if an enemy tried to enter there would be gunfire raining down upon them. At the time of the attack, Pearl Harbor was about 22,000 acres in size and housed most of the Pacific fleet because it was the ideal place to defend against enemy ships.